Re: [RFC][PATCH v12 4/8] Add DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE to glibc DSOs (bug 22745)

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 08/07/2021 13:32, Vivek Das Mohapatra via Libc-alpha wrote:
> libc.so, libpthread.so etc should have the new unique-dso-by-default
> flag set to allow dlmopen to work better (libc et al instance shared
> by default when DSOs dlmopened into a new namespace).

The patch looks ok, some comments below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>


> ---
>  Makeconfig                |  3 +++
>  Makerules                 | 18 ++++++++++++++++-
>  config.make.in            |  1 +
>  configure                 | 42 ++++++++++++++++++++++++++++++++++++---
>  configure.ac              | 31 ++++++++++++++++++++++++++---
>  elf/Makefile              |  3 +++
>  elf/dynamic-notes.c       |  4 ++++
>  extra-lib.mk              |  3 +++
>  htl/Makefile              |  3 +++
>  iconvdata/Makefile        |  3 +++
>  iconvdata/extra-module.mk |  4 ++++
>  nptl/Makefile             |  7 ++++++-
>  12 files changed, 114 insertions(+), 8 deletions(-)
>  create mode 100644 elf/dynamic-notes.c
> 
> diff --git a/Makeconfig b/Makeconfig
> index efc7351d71..baa893840e 100644
> --- a/Makeconfig
> +++ b/Makeconfig
> @@ -398,6 +398,9 @@ LDFLAGS-lib.so += -Wl,-z,now
>  # Extra flags for dynamically linked non-test main programs.
>  link-extra-flags += -Wl,-z,now
>  endif
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-lib.so += -Wl,-z,unique
> +endif
>  
>  # Command to run after every final link (executable or shared object).
>  # This is invoked with $(call after-link,...), so it should operate on

Ok.

> diff --git a/Makerules b/Makerules
> index 596fa68376..66c1251754 100644
> --- a/Makerules
> +++ b/Makerules
> @@ -581,7 +581,8 @@ $(common-objpfx)shlib.lds: $(common-objpfx)config.make $(..)Makerules
>  		 PROVIDE(__start___libc_IO_vtables = .);\
>  		 __libc_IO_vtables : { *(__libc_IO_vtables) }\
>  		 PROVIDE(__stop___libc_IO_vtables = .);\
> -		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@'
> +		 /DISCARD/ : { *(.gnu.glibc-stub.*) }@' \
> +	      -e 's/^.*\*(\.dynamic).*$$/   .dynamic : { *dynamic-notes.os(.dynamic) *(.dynamic) }/'
>  	test -s $@T
>  	mv -f $@T $@
>  common-generated += shlib.lds

Ok.

> @@ -636,6 +637,16 @@ build-shlib-objlist = $(build-module-helper-objlist) \
>  # Also omits crti.o and crtn.o, which we do not want
>  # since we define our own `.init' section specially.
>  LDFLAGS-c.so = -nostdlib -nostartfiles
> +
> +# The stub dynamic-notes.os should not have weak/undefined symbol magic in it.
> +# It's not really part of the internals, rather it is a vector for linker magic
> +# which we need when the linker isn't new enough:
> +%/dynamic-notes.os: CPPFLAGS += -UMODULE_NAME
> +
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-c.so += -Wl,-z,unique
> +endif
> +
>  # But we still want to link libc.so against $(libc.so-gnulib).
>  LDLIBS-c.so += $(libc.so-gnulib)
>  # Give libc.so an entry point and make it directly runnable itself.

Ok.

> @@ -706,6 +717,11 @@ $(common-objpfx)linkobj/libc.so: $(common-objpfx)linkobj/libc_pic.a \
>  	$(build-shlib)
>  	$(call after-link,$@)
>  
> +ifneq ($(ld-zunique),yes)
> +$(common-objpfx)libc.so: $(common-objpfx)elf/dynamic-notes.os
> +$(common-objpfx)linkobj/libc.so: $(common-objpfx)elf/dynamic-notes.os
> +endif
> +
>  ifeq ($(build-shared),yes)
>  $(common-objpfx)libc.so: $(common-objpfx)libc.map
>  endif

OK.

> diff --git a/config.make.in b/config.make.in
> index cbf59114b0..8755490c13 100644
> --- a/config.make.in
> +++ b/config.make.in
> @@ -72,6 +72,7 @@ have-cc-with-libunwind = @libc_cv_cc_with_libunwind@
>  fno-unit-at-a-time = @fno_unit_at_a_time@
>  bind-now = @bindnow@
>  have-hash-style = @libc_cv_hashstyle@
> +ld-zunique = @ld_zunique@
>  use-default-link = @use_default_link@
>  have-cxx-thread_local = @libc_cv_cxx_thread_local@
>  have-loop-to-function = @libc_cv_cc_loop_to_function@

Ok.

> diff --git a/configure b/configure
> index 9619c10991..a53243a178 100755
> --- a/configure
> +++ b/configure
> @@ -625,6 +625,7 @@ libc_cv_cc_nofma
>  libc_cv_mtls_dialect_gnu2
>  fno_unit_at_a_time
>  libc_cv_has_glob_dat
> +ld_zunique
>  libc_cv_hashstyle
>  libc_cv_fpie
>  libc_cv_z_execstack
> @@ -6074,9 +6075,38 @@ fi
>  $as_echo "$libc_cv_hashstyle" >&6; }
>  
>  
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support" >&5
> +$as_echo_n "checking for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support... " >&6; }
> +if ${libc_cv_ld_zunique+:} false; then :
> +  $as_echo_n "(cached) " >&6
> +else
> +  cat > conftest.ld.c <<\EOF
> +int x (void) { return 0; }
> +EOF
> +
> +libc_cv_ld_zunique=no;
> +
> +if { ac_try='${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c'
> +  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
> +  (eval $ac_try) 2>&5
> +  ac_status=$?
> +  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
> +  test $ac_status = 0; }; }
> +then
> +  libc_cv_ld_zunique=yes
> +fi;
> +ld_zunique=$libc_cv_ld_zunique
> +rm -f conftest*
> +fi
> +{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_ld_zunique" >&5
> +$as_echo "$libc_cv_ld_zunique" >&6; }
> +
> +
>  # The linker's default -shared behavior is good enough if it
>  # does these things that our custom linker scripts ensure that
> -# all allocated NOTE sections come first.
> +# all allocated NOTE sections come first AND it understands
> +# -z unique should result in DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE
> +# sections in its output.
>  if test "$use_default_link" = default; then
>    { $as_echo "$as_me:${as_lineno-$LINENO}: checking for sufficient default -shared layout" >&5
>  $as_echo_n "checking for sufficient default -shared layout... " >&6; }
> @@ -6119,10 +6149,16 @@ EOF
>        esac
>        shift 2
>      done
> -    case "$libc_seen_a$libc_seen_b" in
> -    yesyes)
> +    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
> +    yesyesyes)
>        libc_cv_use_default_link=yes
>        ;;
> +    yesyesno)
> +      echo >&5 "\
> +shared layout from:
> +$ac_try
> +is OK but -Wl,-z,unique is unsupported so linker scripts are required"
> +      ;;
>      *)
>        echo >&5 "\
>  $libc_seen_a$libc_seen_b from:

Ok.

> diff --git a/configure.ac b/configure.ac
> index 34ecbba540..9369bcbebe 100644
> --- a/configure.ac
> +++ b/configure.ac
> @@ -1372,9 +1372,28 @@ fi
>  rm -f conftest*])
>  AC_SUBST(libc_cv_hashstyle)
>  
> +AC_CACHE_CHECK([for linker DT_GNU_FLAGS_1/ DF_GNU_1_UNIQUE support],

Maybe a space before ' /'.

> +                libc_cv_ld_zunique, [dnl
> +cat > conftest.ld.c <<\EOF
> +int x (void) { return 0; }
> +EOF
> +
> +libc_cv_ld_zunique=no;
> +
> +if AC_TRY_COMMAND([dnl
> +${CC-cc} -Wl,--fatal-warnings -Wl,-z,unique -shared -o conftest.ld.so conftest.ld.c])
> +then
> +  libc_cv_ld_zunique=yes
> +fi;
> +ld_zunique=$libc_cv_ld_zunique
> +rm -f conftest*])
> +AC_SUBST(ld_zunique)
> +

I think we can simplify it with:

  old_LDFLAGS="$LDFLAGS"
  LDFLAGS="-Wl,--fatal-warnings -Wl,-z,unique -shared"
  AC_CACHE_CHECK([for linker DT_GNU_FLAGS_1 / DF_GNU_1_UNIQUE support],
                 AC_LINK_IFELSE([AC_LANG_SOURCE([void foo (void) { }])],
                                libc_cv_ld_zunique=yes,
                                libc_cv_ld_zunique=no))
  LDFLAGS="$old_LDFLAGS"
  AC_SUBST(ld_zunique)


>  # The linker's default -shared behavior is good enough if it
>  # does these things that our custom linker scripts ensure that
> -# all allocated NOTE sections come first.
> +# all allocated NOTE sections come first AND it understands
> +# -z unique should result in DT_GNU_FLAGS_1/DF_GNU_1_UNIQUE
> +# sections in its output.
>  if test "$use_default_link" = default; then
>    AC_CACHE_CHECK([for sufficient default -shared layout],
>  		  libc_cv_use_default_link, [dnl

Ok.

> @@ -1410,10 +1429,16 @@ EOF
>        esac
>        shift 2
>      done
> -    case "$libc_seen_a$libc_seen_b" in
> -    yesyes)
> +    case "$libc_seen_a$libc_seen_b$libc_cv_ld_zunique" in
> +    yesyesyes)
>        libc_cv_use_default_link=yes
>        ;;
> +    yesyesno)
> +      echo >&AS_MESSAGE_LOG_FD "\
> +shared layout from:
> +$ac_try
> +is OK but -Wl,-z,unique is unsupported so linker scripts are required"
> +      ;;
>      *)
>        echo >&AS_MESSAGE_LOG_FD "\
>  $libc_seen_a$libc_seen_b from:

Ok.

> diff --git a/elf/Makefile b/elf/Makefile
> index 698a6ab985..9734030c23 100644
> --- a/elf/Makefile
> +++ b/elf/Makefile
> @@ -103,6 +103,9 @@ endif
>  
>  ifeq (yes,$(build-shared))
>  extra-objs	= $(all-rtld-routines:%=%.os) sofini.os interp.os
> +ifneq (yes,$(ld-zunique))
> +extra-objs      += dynamic-notes.os
> +endif
>  generated	+= librtld.os dl-allobjs.os ld.so ldd
>  install-others	= $(inst_rtlddir)/$(rtld-installed-name)
>  install-bin-script = ldd

Ok.

> diff --git a/elf/dynamic-notes.c b/elf/dynamic-notes.c
> new file mode 100644
> index 0000000000..d0b487e970
> --- /dev/null
> +++ b/elf/dynamic-notes.c
> @@ -0,0 +1,4 @@
> +#include <link.h>
> +
> +const ElfW(Dyn) __dynamic_note __attribute__ ((section (".dynamic"))) =
> +  { .d_tag = DT_GNU_FLAGS_1, .d_un.d_val = DF_GNU_1_UNIQUE };

Ok.

> diff --git a/extra-lib.mk b/extra-lib.mk
> index 72f8d2e1df..9051958ec0 100644
> --- a/extra-lib.mk
> +++ b/extra-lib.mk
> @@ -101,6 +101,9 @@ $(objpfx)$(lib).so: $(firstword $($(lib)-map) \
>  				$(addprefix $(common-objpfx), \
>  					    $(filter $(lib).map, \
>  						     $(version-maps))))
> +ifneq ($(ld-zunique),yes)
> +$(objpfx)$(lib).so: $(common-objpfx)/elf/dynamic-notes.os
> +endif
>  endif
>  
>  endif

Ok.

> diff --git a/htl/Makefile b/htl/Makefile
> index cf9d12fc12..c2a25dcd79 100644
> --- a/htl/Makefile
> +++ b/htl/Makefile
> @@ -203,6 +203,9 @@ libc-link.so = $(common-objpfx)libc.so
>  
>  extra-B-pthread.so = -B$(common-objpfx)htl/
>  LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-pthread.so += -Wl,-z,unique
> +endif
>  
>  include ../Rules
>  

Ok.

> diff --git a/iconvdata/Makefile b/iconvdata/Makefile
> index bb3f621b49..4170005322 100644
> --- a/iconvdata/Makefile
> +++ b/iconvdata/Makefile
> @@ -67,6 +67,9 @@ modules	:= ISO8859-1 ISO8859-2 ISO8859-3 ISO8859-4 ISO8859-5		 \
>  ifeq ($(bind-now),yes)
>  LDFLAGS.so += -Wl,-z,now
>  endif
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS.so += -Wl,-z,unique
> +endif
>  
>  modules.so := $(addsuffix .so, $(modules))
>  

Ok.

> diff --git a/iconvdata/extra-module.mk b/iconvdata/extra-module.mk
> index ecaf507624..92c3ab4d7b 100644
> --- a/iconvdata/extra-module.mk
> +++ b/iconvdata/extra-module.mk
> @@ -7,6 +7,10 @@ $(objpfx)$(mod).so: $(addprefix $(objpfx),$(addsuffix .os,$($(mod)-routines)))\
>  		    $(shlib-lds) $(link-libc-deps)
>  	$(build-module-asneeded)
>  
> +ifneq ($(ld-zunique),yes)
> +$(objpfx)$(mod).so: $(common-objpfx)/elf/dynamic-notes.os
> +endif
> +
>  ifneq (,$(extra-modules-left))
>  include extra-module.mk
>  endif

Ok.

> diff --git a/nptl/Makefile b/nptl/Makefile
> index 9b94bfcd31..81353b9455 100644
> --- a/nptl/Makefile
> +++ b/nptl/Makefile
> @@ -375,7 +375,12 @@ CPPFLAGS-tst-pthread-gdb-attach-static.c := \
>  # were launched with an explicit ld.so invocation.
>  tst-pthread-gdb-attach-no-pie = yes
>  
> -	
> +LDFLAGS-pthread.so = -Wl,--enable-new-dtags,-z,nodelete,-z,initfirst
> +ifeq ($(ld-zunique),yes)
> +LDFLAGS-pthread.so += -Wl,-z,unique
> +endif
> +


I think now that we move all symbols to libpthread, there is no need to mark it
as -z,unique (as you do on a subsequent patch in this set).

> +tests += tst-cancelx7 tst-cancelx17 tst-cleanupx4

I think the extra tst-cleanupx4 is a rebase mistake here.

>  
>  ifeq ($(build-shared),yes)
>  tests += tst-compat-forwarder tst-audit-threads
>